In order to avoid run-on sentences (phrases that run together with inadequate punctuation, sometimes called fused sentences), remember that
Every sentence must be followed by the correct terminal punctuation.
This rule may seem obvious, but it can be easy to violate. You can usually correct run-on sentences by breaking them into two or more separate sentences; however, other methods include inserting a comma and a coordinating conjunction (and, but, for, nor, or, so, or yet), inserting a semicolon, or subordinating one clause to another. For the run-on sentence --
There is a blizzard I don't want to go to class.
--one could employ any of the following solutions:
1. There is a blizzard. I don't want to go to class.
The two clauses are separated into two sentences.
2. There is a blizzard, so I don't want to go to class.
The two clauses are separated by a comma and the coordinating conjunction so.
3. There is a blizzard; I don't want to go to class.
The two clauses are separated by a semicolon.
4. Because there is a blizzard, I don't want to go to class.
Because subordinates the first clause to the second.